The production of ready-to-eat cereal products involves the step of cooking raw grain, typically wheat, oat, rice, barley, maize or rye. This is generally followed by one or more of a variety of further processing stages depending upon the type of end product. Examples of such processing includes tempering, flaking, shredding, extrusion, expansion and baking. Thus in the production of shredded wheat, whole wheat berries are cleaned, cooked in water to gelatinize the starch content, cooled, dried and tempered. The tempered cooked berries are shredded by passage between pairs of rollers, one smooth and one grooved, and the shreds formed into biscuits which are then baked to provide the finished ready-to-eat product.
Cooking of wheat on an industrial scale for breakfast cereal manufacture is conventionally carried out as a batch process in which raw, whole grains are cooked. For example, in the cooking of wheat for shredded wheat manufacture, wheat berries are heated in water at or near boiling point, typically for about 30 minutes.
Batch cooking is not however entirely satisfactory. A major disadvantage is the inconsistency of cook of the wheat which is often observed both within and between batches. Thus within a batch there are variations in moisture content between berries and, most importantly, variations in the degree of cooking. Furthermore, inconsistencies within a batch result from the filling and discharge times which means that not all the berries are subjected to elevated temperatures for the same period of time, and from the "dead spots" which exist within the cooking drum, i.e. areas where the stirring devices do not reach, for example near the outlet; any wheat berries which lodge in such areas will tend to be undercooked.
Undercooked berries tend to be hard and brittle; also biscuits made from shredded undercooked berries have a tendency to disintegrate and to rise inadequately during baking. Conversely, overcooked berries are sticky, have poor handling properties and are more difficult to shred. In the case of a batch process in which the proportion of undercooked or overcooked berries is intolerably high, an entire batch needs to be discarded as being unsuitable for further processing. There is thus a need for improved cooking processes which produce a more consistent product suitable for further processing to ready-to-eat breakfast cereals.
Continuous cooking has previously been proposed for ready-to-eat breakfast cereal. However operational problems were encountered and inconsistency of cook remained a problem. Continuous cooking is not in general industrial use in this technical area.
We have now developed a continuous cooking process for grain, particularly wheat, which can be used to produce a product of consistently high quality, in terms of texture and flavor, at least equal to that obtainable by batch methods.